Composite for catalytic distillation and its preparation

ABSTRACT

The present invention relates to a composite for catalytic distillation, comprising a substrate material, and a modifying material and an active material, wherein said substrate material is made of porous materials, said modified material comprises at least one metal oxide, and said active material comprises an active component for a catalytic reaction. The catalytic distillation composite according to the present invention serves as both distillation packings and catalysts, and can allow catalysts to make the best of its efficiency, provide sufficient contact areas between gas and liquid phases, which facilitates mass transfer between gas and liquid phases, boosts effects in both reaction and separation and is liable for filling, removing and utilizing in industries.

This application is a Divisional of application Ser. No. 10/361,084,filed on Feb. 6, 2003, now U.S. Pat. No. 7,226,884, the entire contentsof which are hereby incorporated by reference and for which priority isclaimed under 35 U.S.C. § 120.

FIELD OF THE INVENTION

The present invention relates to a composite material for catalyticdistillation useful in the fields of petrochemical industry, inparticular, it relates to a composite material used for catalyticdistillation columns in catalytic distillation processes, and theprocess for preparing the same.

BACKGROUND ART

Catalytic distillation technology is a recently developed chemicalengineering process, which combines catalytic step with distillationstep, so that reactions and separations are carried out in the samecolumn simultaneously. The process is capable of removing reactionproducts from each reaction-separation unit continuously and making useof reaction heat as the vaporization heat required for carrying outdistillation. The catalytic distillation technology is characterized byhigher conversions, better selectivity, less energy consumption, higherproduct purity, more convenient operation and less investments and soon, which has been widely researched and rapidly developed since the80's. Such a technology first succeeded in the application for producingmethyl t-butyl ether (MTBE) and then become widely used in many otherareas.

A key to the catalytic distillation technology lies in the method bywhich the catalysts are filled into the reaction sections. Catalysts arefilled in many ways which are generally divided into two types one is aseparate way, and the other is an integrated way. The process of theseparate way produces catalysts and distillation packings separately,that is, catalysts are directly manufactured into granulates of variousshapes and sizes, then combined with distillation packings by variousmeans, and finally filled into distillation columns. For example, asdescribed in U.S. Pat. No. 4,443,559 catalysts granules are filled inbulk into textile bags and supported by a stainless steel wired meshcovering having certain openings, which are rolled into cylindricalrolls consisting alternately of wired mesh layer and fabric bag's layerand form composite materials for use in distillation columns. Accordingto another method of filling catalysts with packings in bulk disclosedin U.S. Pat. No. 5,262,012, granular catalysts are mixed with inertfilling media such as ceramic balls, glass beads, hollow and porousballs or cylinders and then filled into columns. The major deficiency ofthe separate filling form lies in unevenly distributed catalysts in thebed, an excessive local pressure drop, poor gas/liquid flow, resultingin a non-uniform mixing, a non-uniform distribution in concentrations,and even undesirable dead corners. Moreover, design and fabrication ofthe composite are complex, the technical requirements are rigid, andfilling and removal of packings are inconvenient, which are unfavorableto its application in the industry.

The process of integrated type combines catalysts and distillationpackings as a whole to form an unitary and uniform element, and then putthe element into a catalytic distillation column. For example, CN1060228describes a catalytic reaction-rectification column, wherein both traysor plates or packings in the column are directly formed by using activematerials containing catalysts, which resolves problems of packing andfilling of catalysts for catalytic rectification columns; however, thedirect use of a catalytic active substances in forming the trays andpackings leads to poor strength thereof, and further, elevatedtemperature and other factors during the production of trays andpackings result in reduction or even lose of catalytic activity. Inaddition, the costs of both the trays and the packings are relativelyhigher.

Take further examples, CN1167009 discloses a mordenite/metal ceramiccomposite, which is prepared by incorporating an uniform layer ofmordenite molecular sieve directly onto the surface of a metallic orceramic substrate which is designed in advance and has an arbitrarilyselected shape and size. CN 1228032 describes a catalytic packing usefulin catalytic distillation process, which is prepared by vapor-depositingand/or spraying at least one active material as catalysts and/orpromoters onto a substrate such as textiles, knitting or sheet-likepackings U.S. Pat. No. 5,235,102 discloses a catalytic distillationprocess for converting a feed stream in gas or liquid phase into desiredproducts; one of the embodiment uses a rigid honeycomb ceramic blockcoated with catalytic active components as packings in a catalyticdistillation column. In all the disclosed processes mentioned above,there always exist the problems: no matter on what a substrate, e.g.metals, ceramics, or textiles, the catalytic active coatings prepared byimpregnation in liquids, vapor-depositing or spraying methods exhibitpoor adhesion strength, which may peel off or be destructed, and thusdamage the performances of catalysts. Accordingly, there still remainsan urgent needs to improve the adhesion strength between a substrate andan active component layer.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide asimple-to-manufacture and ready-to-effect composite which can be used incatalytic distillation processes. The composite when used in catalyticdistillation allows heterogeneous catalytic reactions and distillationor rectification to take place concurrently over it. This novel-type ofcatalytic distillation composite can bring catalytic action into fullplay, provide sufficient gas/liquid contact area, promote mass transferbetween gas and liquid phases, obtain excellent effects in both reactionand separation, and is liable for filling, removing, and utilizing inindustries.

A composite used for catalytic distillation comprises a substratematerial, a modifying material and an active material, wherein saidsubstrate material is made of porous materials, said modified materialcomprises at least one metal oxide, and said active material comprisesan active component for a catalytic reaction.

Preferably the said porous material is selected from porous metals orporous ceramics. Said modifying material is coated onto the surface ofthe substrate material, and said active material is loaded on themodified material, to form an uniform catalytic distillation compositeproviding functions of both reaction and distillation or separation.

The above substrate is a dumped packing or structured packing of porousmetals or porous ceramics with any size or any shape.

In a catalytic distillation process, heterogeneous catalytic reactionstake place concurrently with distillation or rectification over acatalytic distillation composite or catalyst packing, which thusrequires not only that active components should be uniformly andstrongly adhered to the substrate, have better adhesion strength,without peeling off, but also that such a composite or catalyst packinghas an optimal material, shape and structure, in order that somecomponents in the reaction mixture can be separated smoothly.Accordingly, the substrate of this invention preferably consists of astructured packing of porous metals or porous ceramics with any size orany shape which have a porosity ranging from 30 to 60% and a porediameter from 0.1-20 μm, more preferably from 5 to 20 μm. For example,as the porous metal materials, it is prepared to use porous stainlesssteel materials and more preferably a composite of sintered micro-porousmetal material. Aluminosilicate, high magnesium clays or diatomaceousearth and the like can be use as ceramics.

According to the present invention, the structured porous metal packingcan be prepared by combining or assembling porous metal corrugatedsheets. The structured porous ceramic packing can be formed by combiningor assembling porous ceramic corrugated sheets, corrugated porousceramic wired mesh, or porous ceramic fins.

Preferably, the porous metal corrugated sheets have pore diameter of5-20 μm, porosity of 30-40%, thickness of 0.2-1.0 mm, corrugation angleof inclination of 30°-45°, and peak height and pitch of 5-30 mmrespectively. Several pieces of corrugated metal sheet are combined intothe structured porous metal packing. Preferably, said structured porousmetal packing is formed into an integrated structure, having the shapeof disc when the diameter is smaller than 500 mm, having 6 sections tobe pieced together when the diameter is smaller than 800 mm, and having9 sections or more to be pieced together when the diameter is largerthan 800 mm.

The porous ceramic corrugated sheet, porous ceramic wired mesh or porousceramic fin which forms the structured porous ceramic packing of thepresent invention can be manufactured by a conventional method, and ispreferably manufactured by the process comprising the following steps,(1) 60-80 wt % of substrate, 20%-40 wt % distilled water together with10%-20 wt % binder and pore-forming agent are mixed up and ball-milledfor 5-20 hour to form a homogeneously dispersed slurry which is thenadjusted to pH5.0-7.0; (2) the slurry obtained in step (1) isextrusion-formed by means of a predetermined die, for a preferredcorrugated porous ceramic sheet, the die should meet the requirement ofpeak height, pitch and angle of inclination; the preform thus obtainedis trimmed to make the packing have a smooth surface without defectsthereon, and dried at ambient temperature, and is opened several holes;(3) the dried preforms are assembled in such a way that waves orcorrugations in two adjacent corrugated sheets are perpendicular to eachother, and the contacting peaks there-between are bound with the binderto form a complete disc or tray; (4) the assembled packing is sinteredin an oven at 800-1000° C., to obtain the structured porous ceramicpacking, wherein, in step (1), starch is preferably used as the binderand pore-forming agent, and HCl or tetramethyl ammonium hydroxide ispreferably used to adjust pH of the slurry; and in step (3), water glassis preferably used as the binder. Preferably, said structured porousceramic packing is formed into integrated tray if a diameter of smallerthan 500 mm required, or is formed by 6 sections to be pieced togetherif a diameter of smaller than 800 mm is required, or by 9 sections ormore to be pieced together if a diameter of larger than 800 mm isrequired.

Preferably, the structured porous ceramic packings consist of the porousceramic corrugated sheets, which have an uniform microporous structure,a porosity of 30-60%, a pore diameter of 10-181 μm, a wall thicknessbetween 0.8 and 1.2 mm, corrugation angle of inclination of 30°-45°,peak height and pitch of 5-30 mm respectively, and holes or openings of3-6 mm in the wall of corrugated sheets for the purpose of improvingmass transfer.

For achieving better separation effects during catalytic distillation,the substrate according to the present invention preferably has aspecific surface area greater than 400 m²/m³, more preferably 400-800m²/m³ and a void ratio of 70-95%, preferably greater than 90%, and thenumber of theoretical column trays of more than 4 per meter.

It is worth noting that the substrate used in present invention ismodified by surface-treatment, in particular, the substrate is treatedwith a modifying material comprising useful metal oxides to form acoating layer comprising the modifying material in order that thecatalytic active materials can be attached to the substrate efficientlyand firmly. Said metal oxides are selected from the group consisting ofAl₂O₃, SiO₂ or TiO₂. Alumina is preferred, which has several variants.Having stable structure, α-Al₂O₃ is preferred for the purpose of theactive components to be loaded on the substrate used for the compositefor catalytic distillation according to the present invention.Generally, the multiple variants of Al₂O₃ will be transformed intoα-Al₂O₃ when treated to 1100° C. or above. It is the calcinatingtemperature that decides the morphology of Al₂O₃. For example, γ-Al₂O₃is generally obtained when the calcination temperature ranges from 400to 600° C., α-Al₂O₃ when the calcination temperature ranges from 1000 to1200° C.

The performances of the modifying material also depend on particle sizeof the modifying material, generally, an average particle size iscontrolled within 10 μm, preferably below 1 μm.

The substrate is coated with the modifying material by a thermo-chemicalreaction process comprising the following steps:

a) preparing a water-based coating material in which superfine particleswith particle size below 10 μm of the modifying material are dispersed,wherein the ratio of modified material to water is in a range between1:2 and 1:5 and pH of the solution is adjusted to a range between 2 and4;

b) coating the substrate material with the water-based coating materialobtained from step a), the obtained substrate material is subjected todrying and curing treatment to form a modified coat on the surfaces ofthe substrate material.

Preferably, the said process comprises the steps of

1) preparing a water-based coating by using superfine particles selectedfrom alumina, silica or titania of particle size below 10 μm, addingdistilled water with a weight ratio of 1:2-1:5 and stirring untilhomogeneous, adding phosphorous acid to adjust Ph of the solution to2-4, to form a water-based coating material; cleaning and drying thesurface of the substrate;

2) dip-coating the substrate with the water-based material to form auniform coat, and drying at ambient temperature;

3) drying the obtained substrate at 100-120° C.;

4) calcinating the dried substrate at 600-800° C. for 6-12 hours tocarry out curing treatment so as to accelerate chemical reactions andfinally to obtain a layer of uniform and stabilized ceramic coating.During the curing process, oxides on the surface of substrate and incoatings have thermo-chemical reactions to form a compound phase wherebythe coat and metal substrate are firmly bound together.

The active components in the composite of the present invention areselected from the group consisting of metals of group VIII or IB, or amixture thereof, or selected from an acid cation exchange resin or azeolite molecular sieve of Y, X, β- and various modified types. Metalsused as the active components in present invention include elementsselected from copper, silver, gold, rhenium, ruthenium, cobalt, rhodium,nickel, palladium, platinum and a mixture thereof.

In general, these catalytic active components will be evenly coated on astructured porous metal packings having modifying materials. After thesubstrate is coated with modifying material, catalytic active componentscan uniformly and firmly applied onto the modifying material of apre-tailored structured porous metal or ceramic packings by a dip orspray process to form an active layer thereon, and the composite forcatalytic distillations of the present invention is thus obtained.

The present invention provides two methods for forming an active layer,one of which is liquid phase immersion method and the other is a spraymethod.

Said liquid phase immersion is carried out by immersing modifiedstructured porous metal packings in a solution comprising catalyticactive components, the packings are removed from the solution aftercrystallization for a period of 24 to 48 hours, washed and dried. Saidoperation is repeated several times and followed by baking at 400-600°C. for 8-12 hours to obtain a catalytic distillation composite havingboth reaction and distillation or separation functions.

Said spray method is effected by spraying with a prepared catalyticactive components-containing solution onto a modified structured porousmetal packing by means of a sprayer, drying it at 50-150° C., and bakingit at 400-600° C. for 8-20 hours, and then reducing it under a reductivegas such as hydrogen for 10-12 hours to obtain said catalyticdistillation composite.

The composite of present invention is useful for many chemical processesin catalytic distillation field, including, for example, processes ofcatalytic distillation-selective hydrogenation of cracking gas,etherification, ether-splitting, esterification, alkylation,isomerization, dehydration, and hydrolysis and so on.

The catalytic distillation composite of present invention exhibits thefollowing advantages:

1) Attributed to the combination of the substrate, modifying materialand active components, the composite functions as both distillationpacking and catalyst, which provides good performances of separation andreaction, makes catalytic distillation operation going on smoothly andincreases conversion rate and selectivity of catalytic reactions;

2) Comprising a structured porous metal packing as substrate, thecatalytic distillation composite exhibits the nature of metals such asexcellent heat transfer, sufficient strength and toughness. Further, thecomposite can be manufactured and installed in a convenient way;

3) Having a ceramic coat as a modifying material on the substrate aftersurface-treatment, the composite has catalytic active components to befirmly adhered to the substrate and thus avoids lose of activecomponents;

4) Uniform distribution of catalytic active components in the compositeenlarges geographic area of the catalyst so that the catalysts can beutilized more efficiently;

5) The shape and size of the composite is flexible and can be adjustedin accordance with needs or requirements. The same is for activecomponents and their proportions;

6) The composite provides larger porosity and specific area, a reducedpressure drop and much increased mass and heat transfer efficiencies.

PREFERRED EMBODIMENTS EXAMPLE 1

A porous metal sheet of stainless steel substrate (provided by An-TaiTechnology Co. Limited, Chinese Academy of Iron and Steel Research)having uniform microporous structure, pore diameter of 10-20 μm, aporosity of 35% and a wall thickness of 0.5 mm was adopted. The porousmetal sheets were fabricated into corrugated sheets having corrugationangle inclination of 45° and both peak height and pitch of 15 mm by aconventional method for forming corrugated metal sheets. Severalcorrugated metal sheets obtained according to the method mentioned abovewere assembled together wherein two adjacent corrugated sheets wereperpendicular to each other, to form a structured packing tray of φ100×50 mm.

EXAMPLE 2

A structured porous metal packing manufactured in Example 1 was subjectto surface-modification. (1) Superfine alumina powder having particlesize of below 10 μm was adopted, distilled water was added in a weightratio of 1:3 (alumina:water) and the whole was agitated untilhomogeneous, phosphorous acid was then added to adjust pH of thesolution to 2.5 and whereby a water-based coating material was prepared;(2) the structured porous metal packing was surface cleaned and dried;(3) the structured porous metal packing was evenly coated with thewater-based coating material, and dried in air at ambient temperature;(4) the structured porous metal packing was baked in an oven at 110° C.;(5) the dried structured porous metal packing was subject to heattreatment for curing by being baked at 600° C. for 8 hours, to obtain amodified structured porous metal packing.

EXAMPLE 3

The catalytic distillation composite according to present invention wasused in the preparation of ethylbenzene by alkylation of benzene andethylene. The modified structured porous metal packing prepared inExample 2 was loaded with β-zeolite by the liquid phase immersionprocess. β-zeolite with particle size of below 10 μm was used, to whichdistilled was added in a weight ratio of 1:2 (zeolite:water), and thewhole was stirred until homogeneous, nitric acid was then added toadjust pH of the resulting solution to 4, the structured porous metalpacking was then dipped in the solution for 48 hours and removedtherefrom for washing, drying, and crystallizing; and the aboveprocedure of dipping, washing, drying, and crystallizing was repeatedthrice; the thus obtained material was baked at 500° C. for 10 hours toform a porous metal composite for catalytic distillation. The catalyticdistillation composite was then installed in a reaction section of aφ100 mm catalytic distillation column comprising a reaction section of 2m high and a stripping section of 6 m high wherein the latter sectionwas randomly filled with the packings of φ6×6 mm cannon stainless steelrings with openings. The operation conditions were: space velocity (byweight) for ethylene of 0.28 h⁻¹, benzene/ethylene molar ratio of 6:1,and system pressure of 1.8 MPa, and reaction temperature between 150 and180° C. Under these conditions, a good result was obtained with theethylene conversion of 100% and the average selectivity for ethylbenzeneof 98%.

EXAMPLE 4

The catalytic distillation composite according to present invention wasused in the preparation of isopropyl benzene from propylene and benzenethrough alkylation. The catalytic distillation composite was preparedaccording to the process described in Example 1-3, except that theporous metal corrugated sheets were formed into those having a peakheight of 15 mm, pitch of 30 mm, corrugation angle of inclination of 30°and wall thickness of 0.5 mm and further into a φ500×200 mm structuredporous metal packing tray. The obtained catalytic distillation compositewas then installed in a reaction section of a φ500 mm catalyticdistillation column comprising a reaction section and a strippingsection wherein the reaction section was 9 m high, and the strippingsection was 3 m high and was filled with the structured metal packing oftype 250Y(φ500×200 mm). Operation conditions were: space velocity (byweight) for propylene of 0.36 h⁻¹, benzene/propylene molar ratio of 6:1,and system pressure of 0.8 MPa, and reaction temperature between 140 and180° C. Under these conditions, the propylene conversion of 100% and theaverage selectivity for isopropyl benzene of 98% were achieved.

EXAMPLE 5

The catalytic distillation composite according to present invention wasused in a catalytic distillation-selective hydrogenation of a C₃fraction for removing methylacetylene and propadiene (MAPD). Themodified structured porous metal packing fabricated in example 2 wasloaded with catalytic active component Pd by spray coating. A solutionof palladium chloride or palladium nitrate, comprising 0.5 wt % Pd, wasformulated adjusted to pH5.0-6.5. The resulting solution was sprayedonto a modified substrate previously heated to 40-60° C. by using asuitable sprayer and followed by drying at 120° C. The packing loadedwith Pd was baked at 350-500° C., preferably not exceeding 500° C., for10 hour in general, and then treated in a hydrogen gas under anappropriate pressure and a temperature from 60 to 120° C. for a periodof 12 hours for reduction, so as to obtain the catalytic distillationporous composite. The composite was installed in a reaction section of aφ100 mm catalytic in distillation column with 6 m high comprising afraction section, a reaction section and a stripping section wherein thereaction section measured 1 m high into which 20 pieces of φ100×50 mmcatalytic distillation composite obtained above were installed, and therectification and stripping sections each were 5 m high into which φ6×6mm cannon stainless steel rings with openings were randomly filled. Theraw materials were fed from the lower part of the reaction section andproducts came out from the top. The feed had the following composition.

components C₂° C₃° C₃ ⁻ C₃ ⁻⁻ C₃ ^(≡) C₄ C₅ Molar fraction(%) 0.02 2.5072.14 1.08 2.09 19.43 2.72

A test was conducted under conditions of reaction temperature of 40-50°C., reaction pressure of 1.6-1.8 MPa, space velocity by volume of liquidphase feed of 2 h⁻¹ and a ratio between hydrogen and alkyne of 1.1.Results of the test show that the catalytic distillation composite hasgood performances in both reaction and distillation or separation, asevidenced by the fact that contents of both methylacetylene andpropadiene have been lowered to below 3 ppm and the yield of propyleneis up to 103% after catalytic distillation.

EXAMPLE 6

A mixture of 70 wt % of Al₂O₃ and 20 wt % of distilled water was mixedand 10 wt % of starch was added therein. After the mixture was mixed ina ball mill for 6 hours, a uniformly dispersed slurry was formed and wasthen adjusted to pH6 with HCl. The slurry was extrusion molded by usinga designed mold into corrugated sheets (preform) having peak height of 6mm, pitch of 12 mm, corrugation angle of 45°, wall thickness of 0.8 mmand openings of φ4 mm in the wall. The obtained preform was, aftertrimming, dried in air at ambient temperature, then each dried sheet wasassembled together, wherein two adjacent sheets were perpendicular toeach other and the peaks were bound with water glass to form a finishedstructured packing tray of φ100×100 mm. The assembled packing trays werebaked in an oven at 800-900° C. to obtain structured packings used asthe substrate.

EXAMPLE 7

A structured porous ceramic packing fabricated in Example 6 as asubstrate was surface-modified by immersing a φ100×100 mm structuredporous ceramic packing tray in a suspension of aluminum hydroxide for 20hours, taking out, and baking at 1100° C. for 12 hours, during which thethin coating layer comprising alumina hydrate underwent a phaseconversion to obtain a α-type alumina. The substrate which wassurface-modified with α-Al₂O₃ had a specific area of 550 m²/m³.

EXAMPLE 8

A hydrogenation catalyst was prepared by coating the substratecomprising a modifying layer formed in Example 7 with a Pd-containingsolution. An aqueous solution of palladium chloride or palladium nitratecontaining 0.5 wt % of Pd was prepared, adjusted to a pH between5.0-6.5, sprayed onto a modified substrate preheated to 40-60° C., andthen dried at 120° C. The Pd-loaded packing was baked at 350-500° C.,preferably not exceeding 500° C., for 10 hours in general, and thentreated in a hydrogen gas under an appropriate pressure and temperaturefrom 60 to 120° C. for 12 hours for reducing the catalyst, to obtaincatalytic active component-containing packings.

EXAMPLE 9

The structured member obtained in Example 8 for use in a catalyticdistillation column was installed in the reaction section of a φ100catalytic distillation column. In the column, a test of catalyticdistillation for hydrogenation of a C₃ fraction was conducted thoughselective hydrogenation and removal of methylacetylene and propadienecontained in propylene. The catalytic distillation column was 6 metershigh and consisted of a rectification section, a reaction section and astripping section, wherein the reaction section was 1 meter high inwhich 10 pieces of φ×100×100 mm structured porous packing trays wereinstalled, and the rectification and stripping sections were 5 metershigh which were filled with dumped packings of φ6×6 mm cannon stainlesssteel rings with openings. Raw materials were fed from the lower part ofthe reaction section and products came out from the top. The results oftest are shown in Table 1 below.

TABLE 1 location feed Tops bottoms composition C₂ ⁰ 0.02 0.02 mol % C₃ ⁰2.50 4.11 1.46 C₃ ⁼ 72.14 95.87 11.29 C₃ ⁼⁼ 1.08 4 ppm 2.47 C₃ ^(≡) 2.093 ppm 4.72 C₄ 19.43 74.05 C₅ 2.72 6.02 flow(l/h) 10 7.4 2.6temperature(° C.) 25 42 98 pressure(MPa) 2.3 1.75 1.78 H₂/alkyne 0.9Propylene yield(%) 101.9

It can be seen from the results of the test that the structured memberfor catalytic distillation of the present invention has a goodperformances in both reaction and separation as evidenced by the factthat contents in both methylacetylene and propadiene in the overheadproducts have been lowered to below 3 ppm after catalytic distillation.

EXAMPLE 10

The performances of the structured members for catalytic distillationthat had been surface-modified with different types of Al₂O₃ werecompared. Multiple φ100×100 mm structured porous packings fabricated inExample 6 were immersed in a suspension containing aluminum hydroxidefor 20 hours, taken out, and divided into two groups and baked for 12hours at 500° C. and 1100° C. respectively, which result in thatpackings were surface modified with γ-Al₂O₃ or α-Al₂O₃ accordingly.After modification, the modified structured porous ceramic packings werecoated with metal Pd in the same manner as indicated in Example 3. Thetwo groups of structured catalytic distillation members were placed in areaction section of catalytic distillation column separately in thesimilar manner as indicated in Example 4 and tested in separate runs ofcatalytic distillation for hydrogenation of C₃ fraction under conditionsgiven in Example 4. The results are shown in table 2.

TABLE 2 structured member for catalytic distillation γ-Al₂O₃ modifiedα-Al₂O₃ modified specific area (M²/g) 50 10 conversion (%) 99.98 99.96selectivity (%) 46.38 82.44

It can be seen from the results that the structured members used in acatalytic distillation column modified with α-Al₂O₃ have both higherconversion and better selectivity while those structured members used ina catalytic distillation column modified with γ-Al₂O₃ have a highconversion but a poorer selectivity. Thus, according to the presentinvention, using α-Al₂O₃ to modify the surface of structured porousceramic packing for a catalytic distillation column shows better result.

1. A catalytic distillation process, comprising: installing a compositematerial in a catalytic distillation column comprising a reactionsection and a stripping section, and said composite material comprises asubstrate material, a modifying material and an active material, whereinsaid active material comprises an active component for a catalyticreaction; evenly coating said modifying material onto the surface of thesubstrate material; and loading said active material on the modifyingmaterial; wherein said substrate is structured packing made up of porousmetals or porous ceramic materials and can be pieced together and formedinto an integrated structure, and said modifying material comprisesα-alumina.
 2. The catalytic distillation process according to claim 1,wherein said process is catalytic distillation-selective hydrogenationof cracking gas.
 3. The catalytic distillation process according toclaim 1, wherein said process is alkylation.
 4. The catalyticdistillation process according to claim 2, wherein said process iscatalytic distillation-selective hydrogenation of C3 fraction forremoving methylacetylene and propadiene.
 5. The catalytic distillationprocess according to claim 3, wherein said process is the preparation ofethylbenzene or isopropylbenzene by alkylation.
 6. The catalyticdistillation process according to claim 1, wherein said catalyticdistillation column further comprises a fraction or rectificationsection.
 7. The catalytic distillation process according to claim 1,wherein said porous material is selected from porous metals or porousceramics.
 8. The catalytic distillation process according to claim 1,wherein said porous material has a porosity of 20-60% and a porediameter between 5 and 20 μm.
 9. The catalytic distillation processaccording to claim 1, wherein said substrate has a specific area greaterthan 400 m²/m³ and a voidage of 70-95%.
 10. The catalytic distillationprocess according to claim 9, wherein said structured packing isfabricated from porous corrugated metal sheets, porous ceramiccorrugated sheets, porous ceramic wired mesh or porous ceramic fins. 11.The catalytic distillation process according to claim 10, wherein saidporous metal corrugated sheets have a pore diameter of 5-20 μm and aporosity of 30-40%.
 12. The catalytic distillation process according toclaim 11, wherein said porous metal corrugated sheets have a wallthickness of 0.2-1.0 mm, corrugation angle of inclination between 30°and 45° and both peak height and pitch of 5-30 mm.
 13. The catalyticdistillation process according to claim 10, wherein said porous ceramiccorrugated sheets have a pore diameter of 10-18 μm and a porosity of30-60%.
 14. The catalytic distillation process according to claim 13,wherein said porous ceramic corrugated sheets have a wall thickness of0.8-1.2 mm, corrugation angle of inclination between 30° and 45°, bothpeak height and pitch of 5-30 mm, and openings of 3-6 mm in the wall.15. The catalytic distillation process according to claim 1, whereinsaid active component is selected from metals of group VIII or IB andmixtures thereof, an acid cation exchange resin or Y, X, and β-types ofzeolite molecular sieve.